The lepidopteran family noctuidae includes some of the most destructive agricultural pests, such as the genera Heliothis, Helicoverpa, Spodoptera and Trichoplusia. For example, included in this family are the tobacco budworm (Heliothis virescens), the cotton leafworm (Alabama argillacea), the spotted cutworm (Amathes c-nigrum), the glassy cutworm (Crymodes devastator), the bronzed cutworm (Nephelodes emmedonia), the fall armyworm (Laphygma frugiperda), the beet armyworm (Spodoptera exigua) and the variegated cutworm (Peridroma saucia). Juvenile hormone esterase is responsible for the stage-specific metabolism of juvenile hormone in such insects.
Juvenile hormone and juvenile hormone esterase have been studied extensively in the Lepidoptera. In the final larval growing stage of these insects, there is a rapid decline in the juvenile hormone titer which initiates the physiological and behavioral events preceding pupation and adult development. This decline in the juvenile hormone titer appears to be regulated by an increase in degradation by juvenile hormone esterase as well as a reduction of biosynthesis. Juvenile hormone esterase activity is very low in the early stadia of larval growth. Even at the peak activity levels in the blood of the final stadium, the concentration of Juvenile hormone esterase has been estimated at less than 0.1 percent of the total protein. Yet the enzyme has a high affinity for juvenile hormone.
The initial reduction in juvenile hormone titer in the last larval stadium initiates a sequence of events leading to pupation. Powerful and selective chemical inhibitors of juvenile hormone esterase have been used in vivo to demonstrate the developmental consequences of blocking the activity of juvenile hormone esterase. For example, a group of the chemical inhibitors of juvenile hormone esterase are the trifluoromethylketone sulfides, as described by U.S. Pat. No. 4,562,292, issued Dec. 31, 1985, inventors Hammock et al. Treatment in the final larval stadium of the tomato hornworm (Manduca sexta) and other moth larvae with potent inhibitors can block almost all of the blood juvenile hormone esterase activity and cause a delay in the time of metamorphosis, presumably by allowing juvenile hormone to remain present.
Classical methods of protein purification have been inefficient for the large-scale purification of juvenile hormone esterase because the esterase is in picomole amounts even at its peak levels. More recently, a purification method for juvenile hormone esterase from larval blood has been developed. Abdel-Aal and Hammock, Science, 233, pp. 1073-1076 (1986).
There is a need for genes which when produced in expression systems will lead to rapid insect death, disruption of development, and/or cessation of feeding. Recent efforts have centered on the insect specific toxins from Bacillus thuringiensis (Merryweather et al., 1990), from the scorpions Buthus eupeus (Carbonell et al., 1988) and Androctonus australis (Stewart et al., 1991; McCutchen et al., 1991; Maeda et al., 1991) and from the mite Pyemotes tritici (Tomalski and Miller, 1991).